High voltage vacuum tube



July 2, 1940;

W. H. BENNETT HIGH VOLTAGE VACUUM TUBE Filed July 9, 1937 4 Sheets-Sheet1 July 2, 1940. w. H. BENNETT 2,206,553

nma venues VACUUM was Filed July 9, 1937 4 Sheets-Sheet 2 H'Hli lmmrir'Wr III INVENTOR.

mlhrdlmeamz.

y 2, 1940. w.. H. BENNETT 2,206,553

HIGH VOLTAGE VACUUM TUBE Filed July 9, 1937 4 Sheets-Sheet 3 INVENT OR.

M'llardH Bennett.

w. H. BENNETT 6,558

HIGH VQL'I'AGF VACUUM TUBE July 2, 1940.

Filed July 9, 1937 Sheets-Sheet 4 Patented July 2, 1940 UNITED STATESPATENT OFFICE 18 Claims.

My invention relates to high voltage vacuum tubes and particularly tovacuum tubes operating Within the upper voltage range of several hundredthousand volts to a million volts or more.

An object of my invention is the provision of high voltage vacuum tubesarranged to be subjected to large electrical differences of potential ofsuiiicient value to cause formation of cold emission streams, and aninsulating material to prevent the formation of said cold emissionstreams.

Another object of my invention is the provision of a high voltage vacuumrectifier tube adapted to operate at extremely high voltages in theorder of several hundred thousand volts to a million volts or morewithout rupture.

Another object of my invention is the provision of a high voltage X-raytube which may be operated at extremely high voltages in the order ofseveral hundred thousand voltsto a million volts or more withoutrupture.

Another object of my invention is the provision of a portable X-raydevice having a high voltage transformer and a high voltage tube mountedwithin a portable container, so that the X-ray device may be moved aboutto accommodate the uses to which it is to be put.

Another object of my invention is the provision of a high voltage tubefor producing radio active elements, which may be operated at severalhundred thousand volts or higher without rupture.

Another object of my invention is the provision of a high voltage vacuumtube which causes the ions to strike the material which they arebombarding with energy corresponding to substantially twice the voltageon the tube.

Another object of my invention is to provide for stripping the electronsoff the nuclei of the ions during their travel and cause the ions tostrike the material being bombarded with energy corresponding tosubstantially twice the voltage on the tube.

Another object of my invention is the provision of a very thin metalfoil charged at a very high electrical potential and supportedtransversely of the direction of the motion of the ions to strip theelectrons oii the nuclei of the ions and cause the ions tostrike thematerial being bombarded with energy corresponding to substantially twoor more times the voltage on the tube.

Another object of my invention is to provide for making the operatingportion or head of my vacuum tube relatively small, so that it may bereadily adaptable to many uses which would be denied to a relativelylarge operating portion or head.

Other objects and a fuller understanding of my invention may be had byreferring to the following description and claims, taken in combination1 with the accompanying drawings in which:

Figure 1 illustrates a cross-sectional view of a high voltage rectifiertube embodying the features of my invention;

Figure 2 shows a cross-sectional view of an X-ray device which may bemoved about to accommodate the uses to which it is put;

Figure 3 is a cross-sectional view of a high voltage tube arranged toproduce radio active elements; g

Figure 4 is across-sectional view of a. high voltage tube arranged toproduce radio .active' elements, and is designed to cause the ions tostrike the material which they are bombarding with energy correspondingto substantially twice I the voltage on the tube; and

Figure 5 is an enlarged cross-sectional view of the intermediateelectrode shown in the vacuum tube in Figure 4.

My invention applies to high voltage tubes of all kinds and is notlimited to the particular high voltage tubes shown and described herein.

In Figure 1 of the drawings, my invention is shown as being embodied ina rectifying tube indicated by the reference character I0 and comprisesgenerally a vacuum glass container ll having a hot cathode 24 and cooledanode H5.

The right-hand end of the glass container I i is closed by means of asealed head member l2 which abuts against the end of the glass II and issealed thereto by means of a sealing material I3. Attached to the sealedhead member I2 is a vacuum header I4 having a vacuum pipe l5 extendingtherefrom connected to a vacuum pump for exhausting the air from insideof the vacuum tube. I

The anode l6 maybe cooled by passing a cooling fluid through the pipesl1 and H3, which pipes also constitute a support for the anode it. Theanode may be grounded at !9 or at any other suitable connection. Thecathode 24 may be supported by an electrically conducting tube 25, whichis in-turn supported. in longitudinal space relationship to the glass IIby means of insulating brackets 29. The left-hand end of the tube 25 isarranged to fit snugly in a restricted end 26 of the glass. Inside ofthe tube 25 and electrically insulated therefrom is a conductor 21. Theelectrical heating of the cathode 24 is obtained by connecting theconducting tube and be long enough from the high voltage lead-inconductor on the left-hand end of the tube to the ground at the base onthe right-hand end of the tube to prevent spark-over on the outside.Accordingly, the reduced diameter of the tube may be a few feet long ormore in atmosphere. This distance may be considerably reduced byimmersing the tube in oil or other good dielectric material. A pluralityof series connected condensers 45 may be connected across the loadconductors to give a smooth wave form to the load.

Surrounding the cathode 24' is a shield 30 to reduce the field intensityupon the cathode and prevent disintegration thereof. The shieldcomprises 'a hollow cylindrical body having the lefthand end 32 reducedto a relatively small diameter to fit snugly on the outside of the tube25 and to be supported thereby. The forward or right-hand end of theshield is open and is internally bent back upon itself for a relativelyshort distance to form a round end as indicated by the referencecharacter 34. The external surface of the cathode shield 3|] isprotected by a body of insulating material 31 having a round end 38 andsnugly fitting against the external surface of and around the end 34 ofthe cathode shield.

Surrounding the anode l6 and in substantial longitudinal alignment withthe shield 30 is an anode shield 3| comprising a hollow cylindrical bodyhaving its rear end flanged outwardly and suitably connected as at 35 tothe sealed head member l2 in a suitable manner. The shield 3| reducesthe field intensity upon the anode l6 and prevents disintegrationthereof. The left-hand or forward end of the shield 3| is internallybent back upon itself for a relatively short distance to form a roundend 36. Closely fitting the external surface and the round end 36 oftheshield 3| is a body of insulating material 39 having a round end 40. Theinsulating bodies 31 and 39 are substantially identical and each-has itsadjacent ends open to allow the electrons to flow from the cathode 24 tothe anode IS. The insulating bodies 31 and 39 and the supportingbrackets 29 comprise a porous non-vitreous structure. The insulatingbodies 31 and 39 prevent the formation of cold emission streams from theexternal surface of the shields 30 and 3| when the tube is in operation.The nature of the insulating materials 31 and 39 and the brackets 29 andthe process for making same is described in my pending patentapplication, entitled Insulating material, filed July 8, 1937, andSerial No. 152,617. The insulating materials 31 and 39 and the brackets29 may be drilled or worked by a the high potential winding 4| subjectsthe oathode 24 and the anode Hi to a large electrical difference ofpotential. The cathode 24 is heated by the filament winding 28, andemits electrons which travel at high velocity to the anode |6 duringone-half of the alternating current cycle to impress a rectified currentupon the load conductors 43 and 44'. The electrons flow from the cathode24 to the anode |6 during the onehalf cycle when the anode I6 ispositive with respect to the cathode 24. No electrons flow during theother half of the alternating current cycle. Under this arrangement theload conductor 43 would be negative and the load conductor 44 would bepositive.

While the arrangement just described will deliver a high negative steadypotential, the tube maybe changed to enable the arrangement to deliverhigh positive potential. These changes may be effected by exchanging thepositions of the anode l6 and the cathode 24 and suitably cooling theanode and using a separate filament transformer to heat the cathode.

The insulating materials 31 and 39 may be worked to fit closely over theexternal surfaces and around the ends of the shields 30 and 3| toprevent the formation of cold emission streams, so that the tube may beoperated at extremely high voltages in the order of several thousandvolts to a million volts or more without rupturing the tubes.

The focusing of the electrons upon the anode l6 may be determined byvarying the space between the cathode 24 and the anode l6. The shields36 and 3| aid in focusing the electrons as they travel from the cathode24 to the anode l6.

While I have shown only one rectifying tube, two or more may beconnected to provide a fullwave rectification. In installation, therectifier tube should be shielded in some suitable manner by the use oflead or by having it placed in a. separate guarded room. These featuresare not shown as they are usually taken care of when any tube to be usedfor this purpose is installed.

In Figure 2, I illustrate the embodiment of my invention in an X-raydevice which may be moved about to accommodate the several uses to whichit may be put. The X- -ray device comprises generally a tube 56 and ahigh voltage transformer 5| mounted in a portable container 52 carriedby wheels 53. The transformer may be of any suitable type and may besuspended vertically from the cover 54. As illustrated, the cover 54 maybe bolted or otherwise connected to the top of the container 52 by meansof bolts 56.

A fill cap 55 is provided so that the container may be filled with oilor other dielectric material.

The X-ray tube 59 embodies the general construction of the rectifiertube shown in Figure 1 and comprises a glass container having itsrighthand end sealed by means of a head member 64, a cathode 59 and ananode 60 having an inclined forward face 6| to direct the rays upon theobject 8| being X-rayed. The cathode 59 may be electrically connected at69 at the lower end of the suspended transformer and charged to a highpotential. The connection 59 also constitutes a support for theleft-hand end of the tube. The cathode may be heated by a filamentwinding provided in the transformer 5|. The anode 66 may be cooled bymeans of cooling fluid passing through the cooling tubes 62 and 63.These tubes support the anode 60 and pass through the lead header 16 andthe head member 64 which is suitably connected to the lead header 16.Accordingly, the anode 60 is grounded to the container. The buoyanteffect of the oil or other dielectric will approximately support thetube and the joint from the glass to the head member 64 will guide thetube. The cathode 59 is surrounded by a shield 65 and an insulating body61 to prevent the formation of cold emission streams when the tube isoperated at high voltages. The anode 6B is similarly surrounded by ashield 66 and an insulating body 68. The construction of the shields andthe insulating bodies is the same as that described with reference toFigure 1.

The lead header it may be suitably connected by means of clamping boltsll having steel inserts It to the outward end of a cylindrical hollowlead portion 12 which shields the tube and which constitutes a portionof the container. The inner end of the lead portion 12 is flangedoutwardly and engages the internal peripheral edge of the opening in theright hand end of the container 52. In order to prevent leaking of theoil or dielectric material, a good seal may be provided Where the leadportion 72 enters the opening in the container 52 by using an annular.flange Iv suitably fastened against the end of the container 52 by meansof bolts 15, compressing a packing material iii. A suitable flange 78may be employed to make a good seal where the cooling tubes 52 and 63extend through the header F6.

The X-rays may be emitted through an opening 19 provided in the leadportion 72 and strike the object being X-rayed. The opening I9 may be atany convenient position at the bottom as shown, at a side, or at the topof the lead portion I2 and may be covered by a plate 3d to keep the oilor other dielectric material from leaking out. A bracket 83 mounted onthe forward lower-most portion of the container 52 may be provided as asupport for the article being X-rayed. The film for the X-ray isindicated by the reference character 82.

My X-ray device is a self-contained unit. This construction is madepossible by reason of the fact that the insulating material, whichprevents the formation of cold emission streams, permits the operatinghead of the tube to be condensed into a very small space. The entiredevice may be pushed about by the handle 58 and for this reason itpossesses great utility for testing devises using high grade steels orother metals during the process of their manufacture. For instance, inthe manufacture of gun barrels, my X-ray device has great utility,because in the event that an apparent defect is observed while thebarrel is being turned in a lathe, my X-ray machine may be positionedrelative to the gun barrel while in the lathe and used to take a pictureof the apparent defect without removing the gun barrel from the lathewhich consumes a great deal of time and expense. My X ray machine may bewheeled about a factory and used to take X-rays of heavy pieces of steelwhich would be diiiicult to carry into a specially built X-ray room asnow employed for this purpose. As my X-ray device is moved about, it isonly necessary to connect the supplyconductors 5'! to a low voltagesupply source and it is ready for operation. The opening in the leadportion through which the X-rays are emitted may be positioned in anysuitable place about the lead portion to accommodate the several uses towhich the X-ray device may be put. My X-ray device may be operated atseveral hundred thousand volts toa million volts or more and yet be madesmall enough to move about.

Another application of my invention may be embodied into a high voltagevacuum tube ar ranged to produce radio active elements. This embodimentis shown in Figures 3 and 4. The embodiment shown in Figure 3 makes useof posi tive ions introduced into the vacuum tube indicated by thereference character 88. The righthand end of the tube is connected to avacuum header 89 which is in turn connected to a vacuum pipe 90 whichleads to a vacuum pump for removing the air from the inside of the tube83. The vacuum header 89 may be 'abutted against the right hand end ofthe tube 88 and sealed by means of sealing material 99. Attached to theright-hand end of the vacuum header 89 is a positive ion producingdevice 9| arranged to deliver positive ions through the exit orleft-hand open end of the tube 95. The embodiment of the positive ionsproducing device 9i may be of any suitable kind and may be connected toa gas supply indicated by the reference character 92 and energized bythe supply conductor 93 and 94. The gas supply may be hydrogen, helium,or other gas used as a source of bombarding material. The positive ionproducing device 9!! may be grounded to a suitable ground as indicatedby the reference character IZI.

Surrounding the exit end of the positive ions producing tube 95 is ashield 96 which may suitably fasten to the left-hand wall 98 of thevacuum,

header 89 by means of the bolts 91. The lefthand end of the shield 96 isbent inwardly back upon itself for a short distance to. form a round endindicated by the reference character I99. Closely fitting the externalsurface and the forward round end of the shield 95 is an insulating bodyIIlI having a round forward end I92.

Mounted in longitudinal alignment with the positive ion introducing tube95 is a target or anode I03 upon which the ions. may be focused.

The forwardface of the target may be provided with a relatively thinstrip of metal I04 suitably attached thereto by means of silver solderIE5 or other suitable means. Thetarget I93 may be cooled by coolingfluid flowing through the pipes I06 and III! which also constitutes asupport for the target. The cooling tubes I96 and I9? may be supportedin longitudinal spaced relation with the reduced portion of the glasscontainer by means of insulating supports. H3. The cooling tubes I96 andII" are air tight where they pass through the end cover H9 which abutsagainst the left-hand end of the glass container and is sealed theretoby means of the sealing material I29.

The target I03 is provided with a shield Hi9 supported by the tubes I98and IN. The forward or right-hand end of the shield M19 is folded backinternally upon itself and forms a round end H9. An insulating body IIIhaving a round forward end IIZ may be snugly fit over the shield I99.The construction and purpose of the shields 96 and I99, the insulatingbodies I9! and III, and the insulating brackets Iii, are the same asheretofore described with the other embodiments of my invention. Thetarget we may be energized to a high potential with respect to thegrounded positive ion introducing tube 95, by means of a transformer II5 having a primary winding. II? andfla high voltage winding H6grounded'as at H8.

In operation, the positive ions emitted from the positive ionintroducing tube 95 are propelled at a high velocity against the metal5%, when the alternating current Wave is such that a negative potentialexists upon the anode 953 to attract the positive ions. The ions bombardthe metal ltd with energy corresponding to substantially the voltageupon the tube, which ma be in the order of several hundred thousandvolts to a million volts or more. The bombardment is sufficient todisintegrate the metal I94 and produce radio active elements. After thebombardment has been continued for a sufiicient length of time, the tubemay be dismantled and the metal piece I04 removed, after which the metalis treated to render the radio active elements suitable for use.

In Figures 4 and 5, I illustrate another embodiment of my invention forproducing radio active elements in which the ions bombard a materialwith energy corresponding to substantially twice the voltage impressedupon the tubes. In this form of my invention, the glass vacuum containerI25 has a relatively short working head I26 and a relatively long stemI21. The general outline of the glass container I25 is substantially T-shaped. Abutting against the left-hand end of the working head I26 ofthe glass container is a vacuum header I28 which is sealed to the openend of the glass container by means of a suitable sealing material I26.A vacuuml pipe I30, leading from the vacuum head I28, is connected atits lower end to a vacuum pump for removing the air within the glasscontainer I25. In this embodiment of my invention, negative ions areintroduced into the tube for bombarding a material to produce radioactive elements. The device for producing the. negative ions isindicated by the reference character I3I which may be bolted orotherwise suitably connected to the left-hand end of the vacuum headerI28 by bolts I35. The negative ions producing device I3I may be of anysuitable construction and may be energized by the supply conductors I32and I33. The focusing of the negative ions, as they move through thenegative ion introducing tube I38 may be effected by actuating thecontrol lever I34. The negative ions may, for example, be hydrogennegative ions and may be obtained by using water in the tube I36 whichis sealed by means of a sealing material I31 to the bottom of thenegative ion producing device. a

A shield I39 may be mounted around the exit end of the negative ionproducing tube I38. The left-hand end of the shield I36 may be suitablyfastened to the abutting wall of the vacuum header I28 by means ofscrews I40 or by any other means. The right-hand end of the shield I39is open and may be folded internally upon itself for a short distance toform a round end I4I. An insulating body I42 having a round end I43 maybe snugly fit over the external surface of the shield I38 and the roundend I4 I.

Positioned in substantially longitudinal alignment with the negativeions producing tube I38 is a target or anode I50 which may be supportedby cooling tubes I53 and I54. A piece of metal II which is to bebombarded by the ions to produce radio active elements is mounted on theforward face of the target I50 by means of silver solder I52 I50, andhas its right-hand end suitably connected to the inside surface of thesealing head member I44. The left-hand or forward end of the shield I46is folded internally upon itself for a short distance to make a roundend I41. Snugly surrounding the external shield I46 and the round endI41, is a body of insulating material I48 having a round end I49. Theconstruction and purpose of the shields I39 and I46 and the insulatingbodies I42 and I48 are substantially the same as that describedhereinbefore with reference to the other embodiment of my invention.Positioned intermediate the adjacent ends of the insulating bodies I42and I49 and in substantial alignment with the travel of the ions, is anelectrode I60 arranged to strip the electrons ofi the nuclei of the ionsas they travel from the negative ions producing tube I38 to the materialI5I which is being bombarded. An enlarged view of the electrode I60 isshown in Figure 5 and comprises a substantially cylindrical tube memberhaving round ends I64 and I65, supported by means of a conducting rod I6| which is, in turn, supported by means of the insulating brackets I62,in substantally longitudinal spaced relation with the relatively longportion I21 of the glass container. The upper end of the supporting rodI60 is connected to a wire terminal I63 Which extends through and makesa sealed connection with, the glass. A very thin metal foil I61 ispositioned internally of the hollow electrode and substantiallyintermediate the ends thereof. The thin metal foil may be of gold and inorder to facilitate the handling thereof it may be mounted on an annularmember I66 which fits against a shoulder in the inside surface of thecylindrical electrode I60. The metal foil I 61 and the annular member I66 may be held in a fixed position by means of a threaded sleeve I68which threadably engages the threads I69 in the cylindrical electrode.

In the operation of my device a very high positive potential isimpressed upon the conductor terminal I63 and the negative ionsproducing device I3I is grounded as at I13 and the target I50 isgrounded as at the ground I12. The distance between the conductorterminal I63 to the grounded end of the tube must be such as toeliminate flash-over on the external surface of the tube. Accordingly,the distance or length of the glass portion I21 may be in theneighborhood of a few feet or more when the tube is used in atmosphereor shorter when immersed in oil or other good dielectric material. Whenthe conductor terminal I63 is impressed with a relatively high positivepotential and the negative ion producing device I3! is in operation, abeam of negative ions will emerge from the negative ions introducingtube I38. These negative ions will proceed toward the intermediateelectrode I60 and strike the gold foil I61 which is positionedtransversely of the line of travel of the ions. When the ions passthrough the foil, the electrons are stripped oif the nuclei of the ionsand leaves positively charged ions. These positively charged ions uponemergence through the foil still retain energy corresponding to the fullvoltage applied to the tubes minus the absorption of the foil. Thepositively charged ions upon leaving the gold foil proceed toward thetarget I50 and bombard the material I5I to make radio active elements.In going to the target I50 the ions are given additional energycorresponding to the voltage of the tube because they are now positiveions. Therefore, the ions arrive at the material I5I with energycorresponding to substantially twice the voltage of the tubes minus theabsorption of the foil I61. The focusing of the ions as they leave thenegative ions introducing tube I38 may be controlled by the controllever I34 upon the ion producing device I3I, and in the embodiment of myinvention the focusing may be such that the ions are scattered when theystrike the gold foil I61 to prevent damage thereto, but are concentratedat a point where they strike the material l5! to produce effectivedisintegration. V

If negative atomic ions of elements with higher atomic numbers thanhydrogen be used, the increase in energy during the acceleration fromthe intermediate electrodes R60 to the target I50 can be made muchlarger than for hydrogen, since there are more electrons which can bestripped ofi each ion when it passes through the gold foil it'd. Thus,if mercury be used in the tube l3? instead of water, the ions willpossess substantially 80 times the energy corresponding to the voltageon the tube when water is used. When mercury is used in the tube I38,the negative ion producing device l3l must be modified to take care ofthe focusing of the ions.

In the embodiment of my invention, the operating hand may be very smalland yet operate under very high voltages in the order of several hundredthousand volts to a million volts or more. The reduction in size of theoperating head is made possible by my insulating material M2 and MS andinsulating brackets 602 which prevent the formation of cold emissionstreams when the tube is under operation. The operating head ofsubstantially the size of that illustrated in the drawing of Figure 4may be operated successfully without rupture up to 400,000 volts. Uponremoval of the insulating material, the tube would fail at approximately82,000 volts, all metal parts remaining in the same position. Theinsulating bodies E42 and its will stand 409,000 volts with a thicknessof approximately 5 millimeters. The pressure in the vacuum tube was lessthan onetenth micron of mercury. After the bombardment by the ions uponthe metal MI is continued for a sufficient length of time, the tube maybe dismantled or opened at the connection M5 and the metal 85! removedand treated to render the radio active elements suitable for use.

By reason of the fact that my insulating material prevents the formationof cold emission streams, the operating portion or head of my vacuumtube may be made relatively small, so that they may be readily adaptableto many uses which would be denied to a relatively large operatingportion or head. The insulating material will withstand bombardment invacuum by electrical particles having a higher energy than that requiredto rupture glass, quartz, or porcelain. The insulating material may beWorked by a cutting tool and made to fit snugly over metal surfaces andelectrodes in vacuum in order to eliminate open evacuated volumes nextto metal surfaces at which high negative electric fields exist. Theinsulating material has a high porosity and permits rapid evacuation andelimination of gas which may accompany the initial application of highvoltage due to local electrical disturbances such as sparks or thebombardment by high velocity electrical particles. After assembling thetubes, they are evacuated. During the period of evacuation, the tubesmay be baked at approximately 500 degrees centigrade. In this manner theresidual gas pressure due to the insulating material, after baking, doesnot seriously exceed that due to the metal parts of the same size.

The insulating material may be used for the insulating support for wiresand electrodes in any kind of vacuum tube, and is especially convenientbecause it can be machined or worked after firing, so that warps andcontractions due to firing are eliminated. 1

Although I have described my invention with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and thecombination and arrangement of parts may be resortedto without departing from the spirit and the scope of the invention ashereinafter claimed.

I claim as my invention:

1. A high voltage vacuum tube comprising, in combination, a vacuumcontainer, spaced negative electrodes operatively mounted in the vacuumcontainer, one of said electrodes having means extending in the tube forintroducing negative ions in the tube, another of said electrodes havingmeans mounted in the tube and arranged to be bombarded by the ions, ahollow cylindrical metal shield electrically connected with andsurrounding the exit of the negative ion introducing means which extendsinto the tube, a second hollow cylindrical metal shield electricallyconnected with and surrounding the bombarded means, said shields havingspaced adiacent rounded ends and mounted in substantial alignment witheach other, an insulating material closely fitting the external surfacesof each of said metal shields to prevent the formation of cold emissionstreams, so that the tube may be operated at extremely high voltages, apositively charged electrode mounted in the tube intermediate the saidspaced adjacent ends of the shields and in alignment with the path ofthe ions traveling from the ion introducing means to the bombardedmeans, and means mounted on the positive electrode for stripping theelectrons off the nuclei of the ions, and leaving positively chargedions which are given additional energy corresponding to the voltage onthe tube, with the result that the ions strike the bombarded means withenergy corresponding to twice the voltage of the tube minus theabsorption of the stripping means.

2. A high voltage vacuum rectifying tube comprising, in combination, avacuum container, a hot cathode and an anode operatively mounted in thevacuum container, a hollow cylindrical metal shield surrounding thecathode and electrically connected thereto, a hollow cylindrical metalshield surrounding the anode and electrically connected thereto, saidshields being in substantial alignment with each other and having theirspaced adjacent ends rounded, and an insulating material closely fittingthe external surfaces and the rounded ends of each of said shields toprevent the formation of cold emission streams, so that the tube may beoperated at extremely high voltages, said insulating material having aporous non-vitreous structure which may be worked with a cutting tool toclosely fit the shields.

' 3. A high voltage vacuum tube arranged to prevent the formation ofcold emission streams which would otherwise occur therein when subjectedto a high electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operatively mounted in the vacuum containerand arranged to be subjected to large electrical differences ofpotential to cause useful electric current to flow therebetween, one ofsaid electrodes having a surface portion from which cold emissionstreams would normally tend to flow under large electrical differencesof potential between said electrodes, and insulating material positionedexternally of the said surface portion to prevent the flowing of saidcold. emission streams, said insulating material having a porousnon-vitreous structure which may be worked with a cutting tool toclosely fit the said surface portion.

4. A high voltage vacuum tube arranged to prevent the formation of coldemission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacum container,spaced electrodes operatively mounted in the vacuum container andarranged to be subjected to large electrical differences of potential tocause useful electric current to flow therebetween, one of saidelectrodes having a surface portion from which cold emission streamswould normally tend to flow under large electrical differences ofpotential between said electrodes, and insulating material positionedexternally of the said surface portion to prevent the flowing of saidcold emission streams, said insulating material having a porousnon-vitreous structure which will withstand 100,000 volts or more perfive millimeters of thickness at a pressure of one-tenth of a micron orless.

5. A high voltage vacuum tube arranged to prevent the formation of coldemission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operativelymounted in the vacuum containerand arranged to be subjected to large electrical differences ofpotential to cause useful electric current to flow therebetween, each ofsaid spaced electrodes having a metal body with open adjacent endsthrough which said useful current passes, and insulating materialpositioned externally of each said metal bodies to prevent the flowingof cold emission streams therefrom, said insulating material having aporous non-vitreous structure which may be worked with a cutting tool toclosely fit the said metal bodies.

6. A high voltage vacuum tube arranged to prevent the formation of coldemission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operatively mounted in the vacuum containerand arranged to be subjected to large electrical differences ofpotential to cause useful electric current to flow therebetween, each ofsaid spaced electrodes comprising a metal body with open adjacent ends,said adjacent ends having a curved surface at the shortest distancebetween said metal bodies, and an insulating material closely fittingthe external surface of each of said metal bodies to prevent theformation of said cold emission streams, said insulating material havinga porous non-vitreous structure which may be worked with a cutting toolto closely fit the said metal bodies.

7. A high voltage vacuum tube arranged to prevent the formation of cold,emission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operatively mounted in the vacuum containerand arranged to be subjected to large electrical differences ofpotential to cause useful electric current to flow therebetween, each ofsaid spaced electrodes having a hollow cylindrical metal body with openadjacent ends mounted in substantial alignment with each other, saidadjacent ends having a curved surface at the shortest distance betweensaid metal parts, and an insulating material closely fitting theexternal surfaces of each of said metal bodies to prevent the formationof said cold emission streams, said insulating material having a porousnon-vitreous structure which may be worked with a cutting tool toclosely fit said metal bodies.

8. A high voltage vacuum tube arranged to prevent the formation of coldemission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operatively mounted in the vacuum containerand arranged to be subjected to large electrical differences ofpotential to cause useful electric current to flow therebetween, one ofsaid spaced electrodes having means extending in the closely fitting theexternal surfaces of each of said metal shields to prevent the formationof cold emission streams, said insulating material having a porousnon-vitreous structure which may be worked with a cutting tool toclosely fit the said metal shields.

9. A high voltage vacuum tube arranged to prevent the formation of coldemission streams I which would otherwise occur therein when subjected toa high electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operatively mounted in the vauum containerand arranged to be subjected to large electrical differences ofpotential to causeuseful electric current to flow therebetween, one ofsaid spaced electrodes having means extending in the tube forintroducing negative ions in the tube, another of said spaced electrodeshaving means mounted in the tube and arranged to be bombarded by theions, a hollow cylindrical metal shield electrically connected with andsurrounding the exit of the negative ion introducing means which extendsinto the tube, a second hollow cylindrical metal shield electricallyconnected with and surrounding the bombarded means, said shields havingspaced adjacent ends and mounted in substantial alignment with eachother, and an insulating material positioned externally of each of saidmetal shields to preventthe formation of cold emission streams, saidinsulating material having a porous non-vitreous structure which may beworked with a cutting tool to closely fit the said metal shields.

10. A high voltage vacuum tube arranged to prevent the formation of coldemission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operatively mounted in the vacuum containerand arranged to be subjected to large electrical differences ofpotential to cause useful electric current to fiow therebetween, one ofsaid spaced electrodes having means extending in the tube forintroducing positive ions in the tube, another of said spaced electrodeshaving means mounted in the tube and arranged to be bombarded by theions, a hollow cylindrical metal shield electrically connected with andsurrounding the exit of the positive ion introducing means which extendsinto the tube, a second hollow cylindrical metal shield electricallyconnected with and surrounding the bombarded means, said shields havingspaced adjacent ends and mounted in substantial alignment with eachother, and an insulating material positioned externally of each of saidmetal shields to prevent the formation of cold emission streams, saidinsulating material having a porous non-vitreous structure which may beworked with a cutting tool to closely fit the said metal shields.

11. A high voltage vacuum tube arranged toprevent the formation ofcold'emission streams which would otherwise occur therein when subjectedto a high electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operatively mounted in the vacuum containerand arranged to be subjected to large electrical diiterences ofpotential to cause useful electric current to flow therebetween, one ofsaid electrodes emitting negative atomic ions of an element with ahigher atomic number than hydrogen, the said negative ion emittingelectrode having a surface portion from which cold emission streamswould normally tend to flow under large electrical differences ofpotential between said electrodes, and insulatingmaterial positionedexternally of the said surface portion to prevent the flowing of saidcold emission streams, said insulating material having a porousnon-vitreous structure which may be worked with a cutting tool toclosely fit the said surface portion.

12. A high voltage vacuum tube comprising, in combination, a vacuumcontainer, spaced negative electrodes operatively mounted in the vacuumcontainer, a positively charged electrode operatively mounted betweenthe negative electrodes, one of said negative electrodes emittingnegative ions, said positively charged electrode having a thin metalfoil supported transversely of the direction of the motion of the ionsto strip the electrons off the nuclei of the ions and cause the ions tostrike said other negative electrode with energy corresponding tosubstantially twice the voltageon the tube.

13.- A high voltage vacuum tube comprising, in combination, a vacuumcontainer, spaced negative electrodes operatively mounted in the vacuumcontainer, a positively charged electrode operatively mounted betweenthe negative electrodes, one of said negative electrodes emittingnegative ions, said positively charged electrode having a thin gold foilsupported transversely of the direction of the motion of the ions tostrip the electrons off the nuclei of the ions and cause the ions tostrike said other negative electrode with energy corresponding tosubstantially twice the voltage on the tube.

14. A high voltage vacuum tube arranged to prevent the formation of coldemission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacuumcontainer, two spaced electrodes and an intermediate electrodeoperatively mounted in the container in substantially straightalignment, said spaced electrodes being grounded and said intermediateelectrode being subjected to a high positive electrical potential, eachof said spaced electrodes having a surface portion from which coldemission streams would normally tend to flow under large electricaldifferences of potential between the intermediate electrode and the twospaced electrodes, and insulating material positioned externally of thesaid surface portions to prevent the flowing of said cold emissionstreams.

15. A high voltage vacuumtube arranged to preventthe formation of coldemission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacuumcontainer, two spaced electrodes and an intermediate electrodeoperatively mounted in the container in substantially straightalignment, said spaced electrodes being grounded and said intermediateelectrode being subjected to a high positive electrical potential, eachof said spaced electrodes having a surface portion from which coldemission streams would normally tend to flow under large electricaldifferences of potential between the intermediate electrode and the twospaced electrodes, and insulating material positioned externally of thesaid surface portions to prevent the flowing of said cold emissionstreams, one of said spaced electrodes emitting negative ions, saidintermediate electrode having a thin metal foil supported transverselyof the direction of the motion of the ions to strip the electrons offthe nuclei of the ions and cause the ions to strike said other spacedelectrode with energy corresponding to substantially twice the voltageon the tube.

16. A high voltage vacuum tube arranged to prevent the formation of coldemission streams which would otherwise occur therein when subjected to ahigh electrical potential comprising, in combination, a vacuumcontainer, spaced electrodes operatively mounted in the vacuum containerand arranged to be subjected to large electrical differences ofpotential to cause useful electric current to flow therebetween, each ofsaid electrodes having a metal shield extending in advance andsurrounding the active part of the electrodes between which the usefulcurrent passes, the advanced end of the said shields having an openingthrough which the useful current passes, a sheath of insulating materialsurrounding each of said metal shields to prevent the formation ofdestructive cold emission currents, said insulating material having aporous non-vitreous structure which may be worked with a cutting tool toclosely fit the said metal shields.

17. A high voltage vacuum tube comprising in combination, a vacuumcontainer, spaced negative electrodes operatively mounted in the vacuumcontainer, a positively charged electrode operatively mounted betweenthe negative electrodes, one of said negative electrodes emitting trodesoperatively mounted: in the vacuum container and adapted to be chargedof one polarity, an intermediate electrode operatively mounted betweenthe spaced electrodes and adapted to be charged of the oppositepolarity, one of the said spaced electrodes emitting ions of onepolarity, said intermediate electrode having ion permeable meanssupported transversely of the direction of the motion of the ions tochange the polarity of the ions which travel with increased energy tosaid other spaced electrode.

WILLARD BENNETT,

